Impulse generator



March 16, 1937. I w-.-A. TOLSON Y 2,074,033

IMPULSE GENERATOR V F iledMaroh 22, 1954 2 Sheets-Sheet 1 FIG.

RCA-2A 5 PICTURE SIGNAL ALL BY-PASS IMPULSE GENERATOR INVENTOFl William1 1. Tolaon.

I March 16, 1937- w. A. ToLs N 3 IMPULSE GENERATOR Filed March 22; 19342 Sheets-5heet 2 IN VBNTOR VVilliamA. Tolso n ATTORNEY 45 istic of myinventionare set forth with particu- Patented Mar. 16, 1937 PATENTOFFICE nvrrrmss GENERATOR William A. Tolson, Westmont, N. J., assignorto Radio Corporation of America, a corporation of Delaware ApplicationMarch 22, 1934, Serial No. 716,839 8 Claims. .(Ci. 250-36) My inventionrelates to impulse generators and more particularly to generators of thetype adapted to provide either saw-tooth current waves or saw-toothpotential waves,

In television receivers of the type utilizing cathode ray tubes astranslating devices for rendering visible incoming radio signalsrepresentative of a view at a distant transmitter, it is expedient, forray-deflection, to apply across the path of the electron stream a fluxor a potential that periodically increases uniformly from a negative toa positive value and then decreases rapidly to the starting potential orvice versa, By reason of the fact that the graph of the flux orpotential amplitude, if plotted against time, re-

sembles the edge of a saw the phrase saw-tooth wave has been generallyadopted in the art as describing either the current or the potentialwave and it is to generators of wavesof this type v that my inventionpertains.

The "ideal wave shape for ray "deflection or scanning purposes in acathode ray tube should be such that theslope of each portion thereof,corresponding to a scanning period, with respect to a reference axis isconstant. Such wave shapes can be obtained with generatorsof known typesbut it has been noted that when an effort is made to utilize either apotential or a current saw-tooth wave in utilization networks such as onthe deflecting plates or in the deflecting coils associated with thecathode ray tube, distortion isintroduced so thatthe actual fluctuatingpotential appearing across the plates or the actual fluctuatingintensity of the magnetic flux departs from ideal conditions. 5,

It is, accordingly,'the principal object of my invention toprovide asaw-tooth wave generator wherein the ideal output wave shape isdistorted to compensate the distortioncaused by a utilization network,and from which the output potential or current may be utilized directlyupon the deflecting plates in a cathode ray tube or in the deflectingcoils for. deflection purposes."

The novel features which I consider charaterlarity in the appendedclaims. The invention itself, however, both as to its organization andits method of operation, together with additional objects and advantagesthereof, will best be up:

derstood from the following description of a speciflc embodiment whenread in connection with the accompanying drawings, in which:

Figure 1 is a diagrammatic view of a portion of a television receivingsystem including a sawtooth wave generator constructed according to myinvention, Q Figures 2 to 8, inclusive, are wave-form graphs to whichreference will be made in explaining the operation of my improvedgenerator, and

Figure 9 is a diagrammatic view illustrating the application of myinvention to a generator that supplies saw-tooth waves toelectromagnetic deflection coils associated with a cathode ray tube.Referring now to Figure 1 of the drawings, a saw-tooth wave generator,to which my invention is applicable, includesanimpulse source I,preferably supplying periodically recurring positive impulses to thegrid 3 of a thermionic driver tube 5 with respect to the cathode 1thereof. The grid, cathode and anode 9 of the driver-tube are connectedto appropriate points ona bleeder resistor Ii which is connected acrossthe terminals of a direct current source (not shown).

By reason of the grid and cathode connections i3 and IS, the driver-tubeis biased negatively considerably beyond the cut-off point andnormallydraws no current betweenimpulses from the impulse source. During theperiod between positive impulses, therefore, a condenser l1, effectivelyconnected in parallel across a resistor .l9 in the'anode circuit of thedriver-tube and a portion of the potential source, acquires a positivecharge at a relatively slow rate. Each positive impulse applied to thegrid of the driver- 'tube abruptly reduces its plate impedance andthecharge on the condenser is dissipated substantially instantaneously.

The positive potential impulses and the potential appearing across theoutput resistor of the driver tube, plotted with respect to the sametime-axis, are exemplified by Figures 2 and 3 in the drawings. It willbe noted thatthe output potential appears as a saw-tooth wave. .Thesegraphs, as well as the additional graphs in the drawings, are for thepurpose of illustrating waveforms only; they do not illustratecomparative amplitudes.

The input circuit of a wave-amplifier tube 2| is connected across. thedriver-tube output resistor IS, a stopping condenser 23 being includedin the connecting network. Connections 25, i5 and 29 extending from thegrid, cathode and anode of the wave amplifier tube, respectively, to thebleeder resistor, supply the tube with appropriate operating potentials.The recurrent potentials across a resistor 3| included in the outputcircuit of the wave-amplifier tube are exemplified byFigure 4 of thedrawings and such potentials are impressed,through a stopping conidenser it, across the input circuit of a third thermionic device 35,hereinafter referred to as the outputtube. The same bleeder resistor llsupplies energizing potentials to the output tube 35 as shown in thedrawings, a choke-coil 31 being included in the anode-supply connection30.

A connection, including a stopping condenser 4i, extends from the anodeof the output tube to a point 43 on an auto-transformer 45, displacedsomewhat from the electrical center thereof, and the terminals of theauto-transformer are connected, respectively,-to the hori-- zontaldeflecting plates 41 and 49 in a cathode ray receiving tube 5|.

" The deflecting circuit for the deflecting plates which includes theautotransformer and theassociated elements is described and claimed inmy copending application Serial No. 737,163, filed July 27, 1934, andassigned to the Radio Corporation of America. s

, The function 01' the deflecting plates is\ to cause the electronstream. in the tube t move horizontally across a fluorescent screen inone direction at a rate corresponding to the slope of the saw-tooth wavein the periods between positive impulses to the generator from theimpulse source and to rapidly return to its starting point upon theoccurrence of the impulse. For

this purpose, the ideal potential wave on the plates should correspondin shape to the potential appearing across the output resistor IQ of thedriver-tube. Unfortunately, however, by reason of inherent limitationsencountered in the design of wave-utilization networks, the potentialappearing across the deflecting plates in the tube, when plotted alongthe same time-axis hereinbefore referred to, appears as shown in Figure5, wherein it willbe noted that the wave shape, at one side of the zeroaxis. differs from that on the other side of the'axis in that the slopeis not constant. Heretofore, all efforts to secure wave-form correctionthrough modiflcation, of the constants of the various elementsdescribed, have been substantially unsuccessful although many attemptshave been made in that direction.

- tain amount of phase shift.

For example, keeping in mind that a saw-. tooth wave, when analyzed intoa Fourier series, is composed of a large number of sine waves, I haveobtained approximate compensation through frequency discriminatingnetworks in they amplifier and/or networks which introduce a cer- Theresults, however, have not been satisfactory since, as stated, thecompensation is only approximate and nothing short of exact compensationwill prevent distortion in the received picture.

In accordance with my invention, therefore, I depart from the usualpractice of trying to secure correction inthe' output circuit of thegenerator or in the coupling networks therein and, instead, I introducea corrective potential early in the system.

specifically, I connect the input circuit of a wave correction tube 55in parallel with the input circuit of the wave amplifier tube 2| and Ialso connect the output'circuitthereof in parallel with the outputcircuit of the said amplifier tube. The grid and cathode of the wavecorrection tube are also connected, as shown in the drawings, toappropriate points on the bleeder resistor II for the purpose ofsupplying a flxed bias potential thereto.

The function of the wave correction tube is to-supply recurrentpotential increments and to More particularly, I so connect the grid ofthe wave correction tube to the bleeder resistor II that it is normallynegatively biased beyond the cut-off potential. When, therefore, thewave correction tube is energized, in phase with the wave-amplifiertube, only the positive peaks of the energizing potential wave give riseto periodic increments of current in the output circuit thereof whichcurrent increments, as will be notedfrom the drawings, must also flow inthe output resistor SI of the wave-amplifier tube.

' The periodic increments of potential appearing across the said outputresistor are exemplified by Figure" 6 f the drawings and the compositepotential wave across the said resistor is exemplifled by Figure 7.

It will be noted from an inspection of Figure 7 that the slope of thewave at one side of the reference axis is not constant and that thedeparture from linearity is the inverse of the departure from linearityof the wave exemplified by Figure 5, it, of course, being understoodthat the relative positions of the said waves, with respect to thereference axis, are reversed.

When the distorted composite wave is impressed upon the output tube theoutput potentials therefrom correspond thereto and the output potentialwave is, therefore, corrected in the direction to compensate for thedistorted wave, exemplified by Figure which otherwise would be impressedupon the deflecting plates. Such being the case the actual potentialwave impressed upon the deflecting plates takes a form exemplifled byFigure 8 of the drawings, thus being truly saw-tooth in shape.

Under certain circumstances the potentials appearing across the outputresistor of the drivertube may not be great enough to drive the grid 'ofthe highly biased wave correction tube sufficiently positive to enableproper derivation of the correction potentials. In such event, it isquite feasible to interpose a voltage lowering resistor 51, shunted by abypass condenser 59, in the anode supply circuit of the wave correctiontube. When this resistor is present the characteristic curve of the tubeis shifted in the zero direction, as is well known to those skilled inthe art, thus enabling smaller positive potentials applied to the gridthereof to cause plate current increments even though the tube is biasedto the cut-off point.

In a specific embodiment of my invention, now in everyday operation, thecircuit components have values as shown in the drawings.

I also wish to make it perfectly clear at this point that my improvedgenerator may be utilized for the purpose of supplying a compensatedsawtooth wave to electromagnetic deflecting coils or the like. Forthispurpose it is only necessary to interpose an additional stage ofresistancecondenser coupled. class A, amplification (not shown, butexemplified by :r, z, in Figure 1) between the wave-amplifler tube andthe output tube and to connect the output circuit of the output tube tothe coils 6i and 88 as shown in Figure 9. Preferably. the output tubefor supplying the aomoae deflecting coils is of the power amplifierpentode type commercially known as RCA 2A5.

From a consideration of the foregoing, it will be apparent that I haveprovided an improved saw-tooth wave generator wherein a correctionfactor is so introduced that true saw-tooth wave potentials or currentsmay be applied therefi om to the ray-deflecting devices associated witha cathode ray tube or to other utilization networks.

Although I have chosen a specific embodiment of my invention forpurposes of explanation, many modifications thereof will be apparent tothose skilled in the art. My invention, therefore, is not to berestricted except insofar as is necessitated by the prior art and thespirit of the appended claims.

I claim as my invention:

1. In combination, a wave-utilization network, a source of periodicallyrecurrent impulses, means for deriving a saw-tooth wave from saidimpulses,- means for amplifying said saw-tooth wave, and means forintroducing distortion into the wave to compensate wave distortion insaid wave-utilization network, said distortion-introducing meanscomprising an electric discharge tube normally biased to beyond thecut-off potential, connections whereby the saw-tooth wave is impressedon the grid thereof with the proper polarity to compensate said wavedistortion, and means for impressing said distorted wave upon said waveutilization network.

2. In combination, means for producing a sawtooth voltage, an electricdischarge tube having an input circuit and an output circuit whichincludes ,a plate impedance unit, means for impressing said voltage uponsaid input circuit, and a second electric discharge tube having an inputcircuit connected in parallel with said first input circuit and anoutput circuit connected in parallel with said plate impedance unit,said second tube being so biased that current flows in its outputcircuit only when saidsaw-tooth voltage is above a predeterminedinstantaneous value. I

3.3m combination, means for producing a saw-tooth voltage, a waveutilization network, means including an electric discharge tube forcoupling said means to said network, a second electric discharge tubehaving an input circuit and an output circuit, and means for impressingsaid saw-tooth voltage upon said input circuit, said output circuitbeing so connected to a point in said'couplingitmeans between said firstdischarge tube and said network that the outputs of said two dischargetubes add. said second tube being so adjusted that its output is changedonly when said saw-tooth voltage is above a predetermined instantaneousvalue whereby there is compensation for distortion produced in saidnetwork.

4. In combination, a wave-utilization network for utilizing saw-toothwaves, means for producing voltage waves having at least approximately asaw-tooth wave form, and a pair of electric discharge tubes having inputcircuits and output circuits connected in parallel, said input circuitsbeing coupled to said wave producing means and said output circuitsbeing coupled to said network, said tubes being adjusted to have unlikeoutputs of such character that they add to produce a substantiallyperfect saw-tooth wave in said network.

5. Apparatus according to claim 4, characterized in that one of saidtubes is biased to function as a substantially non-distorting amplifierwhile the other of said tubes is biased at least to cut-off. i 1

6. In combination, means for producing a sawtooth voltage, an electricdischarge tube which is so biased as to function as a substantiallynondistorting amplifier, a second electric discharge tube which isbiased at least to cut-off potential,

said two tubes being connected in parallel, means for impressing saidsaw-tooth voltage upon the input circuits of said tubes, and means forsupplying the output of said tubes to a wave-utilization network.

- '7. In combination, means fo'rproducing a sawtooth voltage, awave-utilization network, means including an electric discharge tube forcoupling said means to said network, a second electric discharge tubehaving an input circuit and an output circuit, and means for impressingsaid sawtooth voltage upon said input circuit, said output circuit beingso connected to a point in said coupling means between said firstdischarge tube and said network that the outputs of said discharge tubesadd, said second tube being so adjusted that said outputs add to producea sawtooth wave having distortion therein which compensates fordistortion produced in said network whereby a substantially perfectsaw-tooth wave appears in said network.

8. Apparatus according to claim 7, characterized in that said secondtube is biased at least to cut-ofi.

WILLIAM A. TOLSON.

